The amino acid derivative of the formula ##STR1## wherein R.sup.1, R.sup.2, R.sup.3, and R.sup.10 are as defined later, is known to have renin-inhibitory activity and to be useful for the treatment of hypertensions such as essential hypertension, renal hypertension, and malignant hypertention, heart failure, and the like. EP-A-300189 discloses the following synthetic method For preparing said compound. ##STR2## wherein R.sup.1, R.sup.2, R.sup.3, R.sup.4, and R.sup.10 are as defined later.
The aforementioned method is, however, not entirely satisfactory as an industrial preparation method in that a starting material (VI) is relatively expensive and the total yield of the processes as a whole is as low as about 40-50%, thus rendering preparation cost of the object final product amino acid derivatives (I) considerably high.